Crutches are made either to fit under the armpit, or somewhat shorter crutches are made to fit on the forearm. In both types of crutch, it is common to make the main body of the crutch out of a tubular metal and an extendible crutch is received within the main body. The extendible leg can be secured at various different extensions from the main body to accommodate persons of different heights.
Crutches of this type are usually equipped with a rubber cap at the lower end of the leg extension for engaging the ground. They may also be equipped with various resilient padding members on the armpit support or on the hand support. These pads are designed to absorb the shock of the crutch hitting the ground. However, these various expedients have little effect on the impact of the crutch, and do not do much to increase its comfort in use.
In the past, there have been various attempts to provide a crutch with a spring-loaded leg. The intention behind these proposals is to reduce the shock of the impact of the crutch on the ground. Examples of such proposals are shown in various earlier U.S. Letters Patent.
While these various proposals would have been more or less effective for the purpose intended, they would have required the user to purchase new crutches equipped with the spring-loaded feature and discard the existing rigid crutches. The resulting expense of this would have substantially interfered with the sales and use of such spring-loaded crutches. In fact, few examples can be found of such spring-loaded crutches ever having been in use, notwithstanding their significant advantages.
Clearly, however, the principal disadvantage of these proposals would be overcome by providing a conversion kit which enables the owner of an existing standard type rigid crutch to convert it to a resilient or spring-loaded crutch. The provision of such a kit presents certain obvious difficulties. It must be capable of being readily understood and assembled by unskilled persons or even by persons with some degree of infirmity or disability. It must be a kit such that it can be attached to an existing rigid crutch without the need for any special machining, welding or other sophisticated fastening means. Finally, the kit must be such that it has only a minimum number of parts so that it can be manufactured and sold at a reasonable price.
For simplicity, regular coil springs can be used in the kit for resilience. However, other devices can provide a degree of resilience. These may include a rubber sleeve, an hydraulic device, or pneumatic device, or a synthetic member such as polyurethane or the like. Conceivably, some form of magnetic device might also be used for the purpose.